1. Field of the Invention
The present invention relates generally to data recording, and more specifically to a system and method for multi-level recording in a partial response channel.
2. Related Art
Conventional recording techniques use saturation recording to store information on the recording media. Saturation recording techniques typically store the information in a two-level (i.e., binary) form, using digital data encoding methods to mark the recording medium. The process used to encode the data is limited to codes requiring no more than two, or possibly three, symbol amplitudes. Thus, such techniques provide limits to data storage capacity and transfer rates of the medium.
The most common signal processing technique employed in saturation recording is run-length limited coding and peak detection. The application of more advanced methods of coding, such as partial response maximum likelihood (PRML) sequence detection has recently been considered for saturation recording applications. PRML techniques provide an increase in recording density and reliability over runlength limited codes and peak detection.
Significant advances in electron trapping materials have lead to the development of a storage medium that provides a linear response characteristic. Such a linear response characteristic provides an advantage over saturation-type media in that it adds an analog dimension to the storage capacity of the medium. Because the response is linear, the electron trapping material presents the ability to encode information in two dimensions--amplitude and phase. As a result, the storage medium is no longer confined to storing binary or tri-level data. Instead, the concept of M-ary, or non-binary, data coding and storage is provided. The increased symbol alphabet allowed by such encoding provides the opportunity to increase dramatically the data recording density and transfer rate of the storage device. For example, the potential storage capacity of a single 51/4 inch disk can be extended to several gigabytes if that disk were to be implemented using the electronic trapping materials.
Examples of materials that can be used as the storage media for M-ary storage are described in U.S. Pat. Nos. 4,915,982, 4,834,536, and 4,830,875. Other materials useful as the storage media are disclosed in U.S. Pat. Nos. 4,839,092 and 4,806,772, and 4,842,960. Examples of an optical disk and an optical disk drive incorporating electron trapping materials for data storage are disclosed in U.S. Pat. Nos. 5,142,493 and 5,007,037, respectively. The full disclosure of each of these Patents is incorporated by reference herein.